Power Generation: 6 Problem Areas for Corrosion During a Shutdown

There are six general areas within most power generation plants that may experience problems due to corrosion:

1.  TURBINES

2.  BOILER WATER/STEAM SIDE

3.  GENERATORS

4.  FLUE GAS SIDE

5.  WATER/STEAM SIDE

6.  MISCELLANEOUS EQUIPMENT

 

Increasing Shutdown Periods

We are increasingly seeing extended shut down periods for power stations. This are due to a number of reasons including. 

  • For maintenance or repair
  • Due to excess capacity
  • As Standby in case of break down
  • Partial shut down due to excess capacity
  • Hold until start up
  • 'Extended cold standby" (ECS)

During shutdowns, all equipment must be preserved in the 'As Left' condition till there is a need to activate them. When needed, they should be capable of going 'On-Line' immediately.
When a power plant is not in operation, many components within the plant are subject to corrosion. Corrosion occurs due to the presence of moisture in the air. Moisture accelerates the rate of corrosion leading to malfunctions and the deterioration of parts and components such as Turbines, Power Generators, boilers, condensers etc.Rate of corrosion accelerates, when Relative Humidity crosses the critical level of 40%. Above this level industrial pollutants, like Sulphur-Di-Oxide, also, enhance the corrosion rate as the Corrosion is faster when surfaces are exposed to polluted air in combination with high relative humidity.Hence, if the relative humidity of the area where expensive equipment is stored can be restricted to below 40% then all equipment like generator, turbines and their components can be maintained in well-preserved condition for immediate activation, whenever required.


Dehumidification is used to control condensation. 

Dehumidification involves drying the air by actually removing moisture from it. Removal of moisture from the air lowers the relative humidity of the area effectively arresting corrosion and microbial growth. During turbine storage proper dehumidification, ensures minimum deterioration of all internal systems.Recommendations: Relative Humidity during Power Plant Standby should be maintained at 35-40% RH at 24°C to minimize the loss due to corrosion.